The field of the present invention is apparatus and methods for utilizing a permanent magnet to generate useful electrical power. More particularly, the invention relates to apparatus and methods wherein a permanent magnet is movable relative to a conductor to induce a voltage or electromotive force (e.m.f.) therein. The conductor is connectable in an electrical circuit including a power-consuming electrical load to supply an electrical current flow to the latter. The relationship of the permanent magnet and conductor is selectively adjustable to control the voltage induced in the latter.
Conventional dynamos utilizing permanent magnets are known which are adjustable to control the voltage developed for application to an external electrical load. One such conventional dynamo comprises a stator member carrying an electrical load coil. The load coil includes conductors which are connectable to an external electrical load. In order to adjust the voltage induced in the load coil during operation of this conventional dynamo, the stator member is axially movable relative to a rotor member which carries the permanent magnet. The stator member is movable from a high-voltage position in radial congruence with the rotor member to a low-voltage position wherein the stator member is positioned axially away from radial congruence with the rotor member.
In order to reduce the voltage developed by this conventional dynamo to substantially zero, it must include provision for axially moving the stator member to a position completely out of radial congruence with the rotor member. Of course, such a provision results in this type of dynamo having a large overall axial dimension and being overly heavy in comparison to its electrical capacity. Further, even when the stator member is moved, axially to a position completely out of radial congruence with the rotor member, some residual magnetic coupling of the permanent magnet and stator member may persist. This residual magnetic coupling may cause a parasitic torque resisting rotation of the rotor member even though the dynamo is generating no useful electrical power.
Still further, this conventional dynamo must include means for conducting the generated voltage and current flow from the load coil, which moves with the stator member, to an external electrical load. This necessary function is most often fulfilled by the use of multistrand conductors which are sufficiently flexible to allow axial movement of the stator member relative to the remainder of the dynamo. While such multistrand flexible conductors may provide satisfactory short-term service, they will eventually fail with use as the individual strands thereof fatigue and break. Consequently, such conventional dynamos require regular inspection and maintenance including replacement of wearing parts such as the flexible multistrand conductors.
Another conventional permanent magnet dynamo comprises an immovable stator member rotatably receiving a two-part rotor member. Each of the two parts of the rotor member defines a like number of radially outwardly disposed magnetic poles which are of sequentially opposite polarity when considered circumferentially. The two parts of the rotor member are relatively rotatable to bring either like or opposite magnetic poles into axial alignment. When like magnetic poles are axially aligned during operation of the dynamo, both the magnetic flux in the stator member and the voltage induced in a load coil carried thereby are maximum values. In order to selectively reduce the voltage level developed by this dynamo, the two parts of the rotor member are relatively rotated to move opposite magnetic poles toward axial alignment. As opposite magnetic poles are moved toward axial alignment, it is believed that a small portion of the magnetic flux from the poles flows directly to opposite poles and does not penetrate the stator member and the load coil carried thereby. The remaining magnetic flux which does penetrate to the load coil induces an e.m.f. therein which is believed to be self-canceling according to vector principles. When the opposite magnetic poles are fully in alignment, the magnetic flux induces opposing e.m.f.'s in the load coil which fully cancel one another electrically so that the dynamo generates zero voltage during operation.
However, this second conventional dynamo is similar to the first conventinal dynamo described hereinabove in that even when its voltage output is zero, it is believed that there remains a magnetic coupling of the rotor member and stator member. Consequently, iron losses and heating of the dynamo result and the rotor member is subject to a parasitic torque resisting its rotation even though no useful electrical power is generated.
In view of the deficiencies of conventional permanent magnet dynamos, it is not surprising that these devices have not received favorable consideration for use in flywheel energy storage systems having a high energy density and very high speed of operation. Such energy storage systems demand a dynamo to be driven by the flywheel which can provide a substantially constant output voltage despite rotational speed variations having a range of two-to-one, or more. Further, the dynamo must present only a very low or substantially zero parasitic torque drag to the driving flywheel when its voltage output is zero and no useful power is being extracted from the storage system. That is, when the system is merely storing energy it should not run down because of internal energy losses to its dynamo. As a result, conventional flywheel energy storage systems have used conventional rotating rectifyer or homopolar dynamos with electromagnetic field excitation. However, these conventional dynamos are expensive to manufacture, complex in their structure and somewhat large and heavy in comparison to their electrical capacity.